GS

Display

void Display( void );

Glut Callback to Draw everything.
It clear the screen, call the GameView
Update(), TargetCamera and Draw() and swap the buffers.
See marblegame.cpp.

Idle

void Idle( void );

Glut Idle Callback .
It is continuously called when events are not
being received. It post a refresh request in order to make the animation
as smoother as possible. It is enabled/disable by the Visible Callback